The present invention relates to antenna receiving structures for reception of GPS and Differential GPS signals.
In present Differential Global Positioning System (DGPS) receivers, separate antenna receiving structures are used for receiving the L-band GPS signals from GPS satellites and for receiving the MF-band differential correction signals from a local beacon. An L-band signal transmitted from a GPS satellite is around 1.575 Giga-Hertz (GHz) and an MF-band signal transmitted from a local beacon is in the 283-325 Kilo-Hertz (KHz) range. The MF-band signal from the local beacon contains differential correction information to supplement the position information provided by the L-band satellite signals to provide enhanced accuracy in position determinations made by a processor in the DGPS receiver.
An L-band antenna receiving structure for receiving and initially processing an L-band GPS signal is shown in FIG. 1. FIG. 1 illustrates a patch antenna 100 typically used for reception of L-band signals from GPS satellites. Other antenna structures for receiving L-band signals are known in the art. The patch antenna 100 comprises a receiving element 101 mounted on a low-loss dielectric slab 102. Receiving element 101 is simply a thin flat patch of conductor. On the underside of the dielectric is a conductive surface that acts as an antenna ground plane 104.
The L-band signal energy received by the patch antenna 100 is coupled to electronic front-end receiver circuitry of a GPS receiver. In particular, coupling is provided comprising a first conductor 107 and a second conductor 109, as shown. First conductor 107 connects receiving patch element 101 to circuitry of a front end receiving subsystem 121. Front end receiving subsystem 121 typically comprises a band pass filter centered at or near the L-band GPS carrier frequency and a pre-amplifier suitable for amplification of the filtered L-band signal. Second conductor 109 connects antenna ground plane 104 to a ground of front end receiving subsystem 121. Front-end receiving subsystem 121 couples the GPS signal to the remainder of a GPS receiver system (not shown) for further processing of the satellite information signal.
In a Differential GPS (DGPS) receiving system, a second antenna receiving structure suitable for receiving differential corrections from a local beacon at MF-band frequencies is provided. An MF-band antenna is connected to a front end receiving subsystem that typically provides a band pass filter centered in the MF band and a low noise amplifier. The differential correction signal from the MF-band receiving structure is directed to the remainder of the DGPS receiving system for further processing of the differential correction signal.
Suitable antenna elements for receiving MF-band signals are known in the art, including voltage probe (E-field) and loop (H-field) antennas. For reasons of size and efficiency, patch antennas are generally unsuitable for reception of the MF-band signals. More particularly, a patch antenna suitable for L-band reception is generally unsuitable for reception of an MF-band signal. Similarly, a probe antenna suitable for reception of an MF-band signal is generally unsuitable for reception of an L-band signal. Thus, separate MF-band and L-band receiving structures are provided in a DGPS receiving system.
The MF-band antenna receiving structure may be housed within a different housing structure as the L-band antenna receiving structure. In some cases they are housed together within the same structure. This is advantageous when, for example, it is desirable to have both the L-band and MF-band antenna receiving structures located in approximately the same position or in the same package. In applications where it is desirable to house the antenna receiving structures together in a relatively small package it becomes problematic to efficiently incorporate two different antenna elements into the package and to avoid unwanted RF-coupling and radiation effects.
For at least these reasons, there is a need for a method and apparatus for receiving both the L-band GPS satellite signals and the MF-band differential correction signals using a single antenna structure.
The present invention provides a method and apparatus for receiving both L-band GPS satellite signals and MF-band differential correction signals using a single antenna structure.
According to the present invention an L-band antenna provides for the reception of L-band satellite signals. The L-band signal is electrically coupled to a front end receiving subsystem by way of an electrical connection that also functions to receive ME-band signals. The receiving subsystem provides an electronic processing path for the L-band signal received by the L-band antenna. The receiving subsystem also provides an electronic processing path for the MF-band signal received by way of the electrical connection. The receiving subsystem isolates the L-band signal from the MF-band processing path and isolates the MF-band signal from the L-band processing path. In this way, the L-band antenna, in conjunction with the electrical connection that receives the MF-band signal, functions as a single dual-band antenna.
These and other aspects, features and advantages of the invention will be more readily understood with reference to the following description of embodiments of the invention and attached drawings. Persons of ordinary skill in the art will appreciate that various embodiments of the invention not specifically described herein fall within the scope of the invention as defined by the appended claims.